The semiconductor industry is constantly producing smaller and more complex semiconductors, sometimes called integrated circuits or chips. This trend has brought about the need for smaller semiconductor packages with smaller footprints, higher lead counts, and better electrical and thermal performance, while at the same time meeting accepted reliability standards.
In recent years a number of microelectronic packages have been produced to meet the need for smaller chip packaging. One such package is referred to as a Chip Scale Package (CSP). CSPs are so called because the total package size is similar or not much larger than the size of the chip itself. Typically, the CSP size is between 1 and 1.2 times the perimeter size of the chip, or 1.5 times the area of the die. One example of a CSP is a product developed by TESSERA® called “MICRO BGA” or μBGA. In a CSP, the semiconductor has a set of bond pads distributed across its surface. A first surface of an insulating, flexible film is positioned over the semiconductor surface. Interconnect circuitry is positioned within the film. Electrical connections are made between the interconnect circuitry and the semiconductor bond pads. Solder balls are subsequently attached to a second surface of the film in such a manner as to establish selective connections with the interconnect circuitry. The solder balls may then be attached to a printed circuit board.
CSPs may be used in connection with memory chips. Memory chips may be grouped to form in-line memory modules. In-line memory modules are surface mounted memory chips positioned on a circuit board.
As memory demands increase, so does the need for increased memory capacity of in-line memory modules. A need has also arisen for materials and methods that lead to increased performance by more closely matching the coefficient of thermal expansion of the materials used in these memory modules. Examples of such in-line memory modules are single in line memory modules or SIMMs and dual in-line memory modules or DIMMs. DIMMs have begun to replace SIMMs as the compact circuit boards of preference and essentially comprise a SIMM wherein memory chips are surface mounted to opposite sides of the circuit board with connectors on each side.
A problem with in-line memory modules is that adding more chips to the circuit board spreads out the placement of the chips on the circuit card and therefore requires reconfiguration of the circuit card connectors and their associated connections on the motherboard, which means replacing the memory card and in some cases the motherboard.
Another problem with current in-line memory modules is that a separate heat spreader must be positioned across a set of memory chips. The heat spreader adds cost to the assembly process and adds significant weight to the module.
To send a signal from one semiconductor module to another typically requires sending a signal along a channel or bus to a semiconductor module's electrical contacts, into the semiconductor module, along lead lines or traces to the semiconductor, and out through another contact terminal. Therefore, each semiconductor in the module requires its own set of electrical contacts and lead lines. Electrical contacts and lead lines for common inputs and outputs, such as power, or the like, are, therefore, duplicated.
Moreover, each lead or trace carrying current generates an electrical field around it, the strength of which is inversely proportional to the distance from the lead. To address interference caused by adjacent leads, current semiconductor module configurations require a grounded lead or trace to be placed between signal leads or traces, to negate the electric field. This problem is exacerbated in semiconductor modules where the leads are packed close to one another.
Furthermore, current semiconductor modules are typically coupled to a motherboard through the use of FR4 (Flame Retardant 4) circuit board edge connectors that slidably engage female connector slots. A FR4 circuit board is a widely-used insulating material for making printed circuit boards and is constructed of woven glass fibers (fiberglass) that are epoxied together. A the high number of contacts on such circuit boards requires a relatively hard force to be applied to the circuit board to insert it into the female connector slot. This high force may damage the circuit board or female slot.
In addition, due to the sheer number of electrical contacts on each module, the motherboard to which the semiconductor module connects must be constructed from six or more layers of channel or bus wiring layered between wafers of insulating material. These buses allow the various computer components to communicate with one another. It would be desirable to decease the number of leads and electrical contacts needed per semiconductor module, which would reduce the complexity of such motherboards by requiring less layers, thereby, substantially lowering the cost of the overall computing system.
In view of the foregoing it would be highly desirable to provide a semiconductor module that addresses the above described drawbacks of existing semiconductor modules.